What if there’s a newer version of clang or a different version of Ubuntu?

There is a new llvm/clang release every 6 months. What to do for newer version?

Visit https://apt.llvm.org/ and locate the equivalent of deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-5.0 main for desired combo of clang/Ubuntu and correspondingly update apt-add-repository ... line in the above instructions.